Keep primary vehicle with no resistance (8)

I believe the answer is:

maintain

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'keep' is the definition.
(I know that keep can be written as maintain)

I don't understand the remainder of the clue.

(Other definitions for maintain that I've seen before include "Keep up - carry on" , "Continue with an opinion" , "declare" , "Keep in safety and protect from harm and decay" , "Claim" .)

I've seen this clue in The Times.

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